Energy efficient controlled magnetic field generator circuit

ABSTRACT

A magnetic waveform generator circuit includes a first switch coupled to a first rectifier element at a first node, a first capacitor coupled, at a second node to the first switch, and to a fourth node, a second capacitor coupled, at a third node to the first rectifier element, and to the fourth node, and an inductor coupled between the first and the fourth nodes. The first switch is operable to be in an ON state during a first time period and in an off state during a second time period. The first switch and the first rectifier element are configured to enable the inductor to generate, during the first and the second time periods, a magnetic field having a waveform resembling a positive half-cycle of a triangular waveform.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.14/680,877, filed Apr. 7, 2015, which claims the benefit of priorityunder 35 U.S.C. § 119 from U.S. Provisional Patent Application61/975,997, filed Apr. 7, 2014, which are incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

The present invention generally relates to signal generators, moreparticularly, to an energy efficient controlled magnetic field generatorcircuit.

BACKGROUND

As radio-frequency (RF) and optical electromagnetic signals do notpropagate well under the ocean surface or through land, alternativecommunication methods are to be used for these environments. There aremultiple alternative options, each having advantages and disadvantages.Therefore, different approaches may be taken depending on applications.For example, some applications may use a tether to communicate by wireor optical fiber, which can impose maneuvering limits or hazardsinvolving physical contact with vehicles or structures. As anotherexample, acoustic communications are often used, but are affected bymultipath and shallow-water resonances, with the consequence that robustacoustic communications have a very low bit rate. Yet, another candidatecan be near-field magnetic communications, which works withlow-frequency signals, to be measurable at longer ranges therebylimiting bit rate, and signals which have a rapid drop off in signalstrength at longer ranges.

Recent undersea systems research has shown that manipulating the shapeof the magnetic field changes over time can provide more information,either for higher bit-rate communications or for difficult-to-countershort-term magnetic pings. This is a departure from traditional magneticfield signal shapes, which are sinusoidal and involve a number of cyclesbecause LC circuit techniques can be used to efficiently vary themagnetic field through a resonance of the LC circuit. Achieving similarenergy efficiency in a magnetic field drive circuit and allowing theshape of each cycle of the waveform to be controlled, for example,amplitude modulated, are desired.

SUMMARY

In some aspects, a magnetic waveform generator circuit includes a firstswitch coupled to a first rectifier element at a first node, a firstcapacitor coupled, at a second node to the first switch, and to a fourthnode, a second capacitor coupled, at a third node to the first rectifierelement, and to the fourth node, and an inductor coupled between thefirst and the fourth nodes. The first switch is operable to be in an ONstate during a first time period and in an off state during a secondtime period. The first switch and the first rectifier element areconfigured to enable the inductor to generate, during the first and thesecond time periods, a magnetic field having a waveform resembling apositive half-cycle of a triangular waveform.

In another aspect, a method for providing a magnetic waveform generatorincludes coupling, at a first node, a first switch to a first rectifierelement, A first capacitor may be coupled, at a second node to the firstswitch, and to a fourth node. A second capacitor may be coupled, at athird node to the first rectifier element, and to the forth node. Aninductor may be coupled between the first and the fourth nodes. Thefirst switch is operable to be in an ON state during a first time periodand in an off state during a second time period. The first switch andthe first rectifier element are configured to enable the inductor togenerate, during the first and the second time periods, a magnetic fieldhaving a waveform resembling a positive half-cycle of a triangularwaveform.

In yet another aspect, A magnetic waveform generator circuit includes afirst switch coupled to a first rectifier element at a first node, asecond switch coupled to a second rectifier element at a second node,and a first capacitor coupled, at a third node to the first switch, andto a fifth node. The magnetic waveform generator circuit furtherincludes a second capacitor coupled, at a fourth node to the secondswitch, and to the fifth node, and an inductor coupled between the firstand the second nodes. The first switch and the second switch areoperable to be in an ON state during a first time period and in an offstate during a second time period. The first switch, the second switch,the first rectifier element, and the second rectifier element areconfigured to enable the inductor to generate, during the first and thesecond time periods, a magnetic field having a waveform resembling apositive half-cycle of a triangular waveform.

The foregoing has outlined rather broadly the features of the presentdisclosure in order that the detailed description that follows can bebetter understood. Additional features and advantages of the disclosurewill be described hereinafter, which form the subject of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionsto be taken in conjunction with the accompanying drawings describingspecific embodiments of the disclosure, wherein:

FIGS. 1A through 1F are diagrams illustrating examples of a magneticwaveform generator circuit, a corresponding timing diagram, and variousoperational phases of the magnetic waveform generator circuit, accordingto certain embodiments;

FIGS. 2A-2B are diagrams illustrating examples of a magnetic waveformgenerator circuit with amplitude modulation capability and correspondingtiming diagrams, according to certain embodiments;

FIGS. 3A-3B are diagrams illustrating examples of an H-bridge magneticwaveform generator circuit and an H-bridge magnetic waveform generatorcircuit with amplitude modulation capability, according to certainembodiments; and

FIG. 4 is a diagram illustrating an example of a method for providing amagnetic waveform generator circuit, according to certain embodiments.

DETAILED DESCRIPTION

The detailed description set forth below is intended as a description ofvarious configurations of the subject technology and is not intended torepresent the only configurations in which the subject technology may bepracticed. The appended drawings are incorporated herein and constitutea part of the detailed description. The detailed description includesspecific details for the purpose of providing a thorough understandingof the subject technology. However, it will be clear and apparent tothose skilled in the art that the subject technology is not limited tothe specific details set forth herein and may be practiced without thesespecific details. In some instances, well-known structures andcomponents are shown in block diagram form in order to avoid obscuringthe concepts of the subject technology.

The present disclosure is directed, in part, to an energy efficientcontrolled magnetic field generator circuit. The subject technology usesa coil electromagnet to establish a variable magnetic field that reachesout a significant distance. This subject solution transfers energybetween energy storage devices (e.g., inductors and capacitors) using aswitching scheme that enables the control of the ramp rate and durationof each cycle of the magnetic field waveform. The ramp rate is the rateof change of the magnetic field, and by varying the ramp rate, amongother things, a triangle wave of selectable amplitude, can be created.The subject technology provides a family of circuits that can accomplishthe energy transfer with substantially low energy consumption. Ideally,the disclosed circuits use no energy if lossless devices such asswitches, capacitors, and inductors were used. In practice, no device isperfectly lossless, so the circuits do draw energy. However, the energyconsumption of the disclosed circuits is substantially low compared tothe generated magnetic field strength.

Traditionally, an efficient approach to generate a magnetic field isusing a series LC resonators circuit that generates a sinusoidalwaveform. There are techniques for varying the average amplitude and/orfrequency of the resonance. These techniques are not single-cyclecontrol techniques. It is understood that resonant LC circuits that workwith many cycles of the waveform to deliver information have a lowerrate of information delivery. By being able to modulate each cycle ofthe waveform, more bits per second can be delivered. In addition, byachieving the control through ramp rate control, the waveform can have atriangle shape which can have higher amplitude, and more importantly, ahigher L2-norm than a sine wave with the same peak slope. The peak slopecorresponds to the maximum voltage that the circuit can tolerate. Thetriangular waveform can achieve a higher signal-to-noise ratio (SNR) fora given maximum voltage in the drive circuit. For sensing applications(e.g., magnetic ping), single cycle control can perform identificationwith a shorter signal duration, requiring higher sophistication and coston the part of the adversary to cancel, and also allowing a shorter dutycycle and thus more stealth and energy efficiency.

FIGS. 1A through 1F are diagrams illustrating examples of a magneticwaveform generator circuit 100A, a corresponding timing diagram 100B,and various operational phases 100C through 100F of the magneticwaveform generator circuit, according to certain embodiments. Themagnetic waveform generator circuit 100A (hereinafter “circuit 100A”)includes a first switch S1 coupled between a first node 102 (hereinafter“node102”) and a second node 104 (hereinafter “node104”), a secondswitch S2 coupled between node 102 and a third node 106 (hereinafter“node106”), a first rectifier element D1 coupled in parallel to theswitch S2, and a second rectifier element D2 coupled in parallel to theswitch S1. The circuit 100A further includes an inductor L coupledbetween node 102 and a fourth node 108 (hereinafter “node108”), a firstcapacitors C1 coupled between nodes 104 and 108, and a second capacitorsC2 coupled between nodes 108 and 106. Node 108 is coupled to groundpotential and capacitors C1 and C2 are precharged to +Vp (e.g., 100V)and −Vp (e.g., −100V).

In one or more implementations, the switches S1 and S2 can beimplemented with semiconductor switches such as transistors (e.g.,bipolar junction transistor (BJT), field-effect transistor (FET)) orother types of switches). The rectifier elements D1 and D2 can besemiconductor diodes (e.g., silicon diodes) or other rectifier elements.The inductor L is a magnetic coil of the magnetic waveform generator andcan have an inductance value of the order of hundreds of micro-Henry(μH), for example, 300 μH, and capacitance values of the capacitors C1and C2 can be of the order of hundreds of micro-farad (μF). The circuit100A can generate a current i in the in inductor L that has an optimizedwaveform, for example, a triangular waveform, by controlling theswitches S1 and S2, as shown in the timing diagram 100B of FIG. 1B.

The timing diagram 100B includes control pulses 110 and 112 applied tothe switches S1 and S2, and a triangular waveform 120 for the current iof the inductor L of FIG. 1A. During a time period T1, switch S1 isclosed and switch S2 is open. During a time period T2, both switches S1and S2 are open, and during a time period T3, switch S1 is open andswitch S2 is closed, and during a time period T4, both switches S1 andS2 are open again. The four phases of switches S1 and S2 can cause thecurrent i of the inductor L run through the ramp-up and ramp-down cyclesto create a full cycle of the triangular waveform 120. More detailedoperational descriptions of the circuit 100A are provided below withrespect to FIGS. 1C through 1F.

The operational phase 100C shown in FIG. 1C depicts the operation of thecircuit 100A of FIG. 1A during the time period T1 of FIG. 1B.Transistors Q1 (e.g., an NPN transistor) and Q2 (e.g., a PNP transistor)are example implementations of the switches S1 and S2 of FIG. 1A. Duringthe operational phase 100C, the transistor Q1 is on and the transistorQ2 is off, and diodes D1 and D2 are both reverse biased by the initialvoltage (e.g., 100V) of the capacitors C1 and C2. The capacitor C1discharges through the transistor Q1 and the inductor L, thereby passinga positive up-ramping (increasing) current i in the inductor L, whichforms the first quarter cycle, corresponding to the time period T1, ofthe triangular waveform 120 of FIG. 1B. In practice, the current i rampsup in a manner which can be closely approximated with a linear ramp whenthe capacitor sizing and switch closure interval are such that thecapacitor voltage remains nearly constant during discharging orrecharging intervals.

The operational phase 100D shown in FIG. 1D depicts the operation of thecircuit 100A of FIG. 1A during the time period T2 of FIG. 1B. During theoperational phase 100D, both transistors Q1 and Q2 and diode D2 are off.The stored energy in the inductor L during the phase 100C, is deliveredto capacitor C2 and charges this capacitor through the diode D1 and theinductor L, thereby passing a positive down-ramping (decreasing) currenti in the inductor L, which forms the second quarter cycle, correspondingto the time period T2, of the triangular waveform 120 of FIG. 1B.

The operational phase 100E shown in FIG. 1E depicts the operation of thecircuit 100A of FIG. 1A during the time period T3 of FIG. 1B. During theoperational phase 100E, the transistors Q2 is on and the transistor Q1and both diodes D1 and D2 are off. During this phase, capacitor C2discharges through the transistor Q2 and the inductor L and induces anegative increasing current in the inductor L, which continues thedown-ramping leg of the triangular waveform 120 until the end of periodT3.

The operational phase 100F shown in FIG. 1F depicts the operation of thecircuit 100A of FIG. 1A during the time period T4 of FIG. 1B. During theoperational phase 100F, both transistors Q1 and Q2 and diode D1 are off,and the capacitor C1 is charged through diode D2 and the inductor L. Thecurrent i of the inductor L is negative and decreasing and reaches zeroas the capacitor C1 is charged nearly to its initial voltage. In thecircuits 100A and 100C through 100F, the drive circuitry, protectioncircuitry, power supplies, and internal resistors (e.g., for theinductor L) are not shown for simplicity. With ideal lossless circuitelements, at the completion of the four switching periods (T1 throughT4), the capacitors would have exactly the same voltage as they had atthe beginning of the four periods. However, because of internalresistors and non-ideal switches and rectifiers, there is some energyloss, with the result that the capacitors do not have exactly theiroriginal voltage after the sequence of four switching periods. Tocompensate for this energy loss, some means of recharging (e.g., atrickle charge or a rapid charge with the inductor disengaged) thecapacitors can be employed to prevent any operation failure due to thenon-idealities. The effect of this deviation from the ideal straightline in the triangular waveform may be compensated for by using, in thereceiver, a demodulator that is matched with the non-ideal waveform.

FIGS. 2A-2B are diagrams illustrating examples of a magnetic waveformgenerator circuit 200A with amplitude modulation capability andcorresponding timing diagrams 210, 212, 214, 216, and 220, according tocertain embodiments. The magnetic waveform generator circuit 200A issimilar to the circuit 100A of FIG. 1A, except for the additionalswitches S3 and S4 and capacitors C3 and C4. The addition of theswitches S3 and S4 and capacitors C3 and C4 enable circuit 200A togenerate a current i in the inductor L with a triangular waveform thatcan be amplitude modulated. The switches S3 and S4 are dipole switchesthat can be set to be connecting at either of two positions A or B. Whenset to be at position A, the switches S3 and S4, allow the capacitors C3and C4 to be connected in series with the capacitors C1 and C2,respectively. When switches S3 and S4 are set to be connecting atposition B, the circuit 200 becomes similar and operates similarly tothe circuit 100A. The switches S3 and S4 can be implemented assemiconductor dipole switches using known transistor or diode switchcircuitry.

When the switches S3 and S4 are set to be connecting at position A, asmentioned above, capacitors C3 and C4 are connected in series withcapacitors C1 and C2 to provide a higher voltage for driving the currenti through the inductor L, which can form the high current amplitude ofthe amplitude modulated waveform, as shown in the timing diagram 220 ofFIG. 2B. In the circuit 200A, the drive circuitry, protection circuitry,power supplies, and internal resistors (e.g., for the inductor L) arenot shown for simplicity

The timing diagrams 210, 212, 214, 216 shown in FIG. 2B are controlpulses applied to switches S1 through S4. The timing diagrams are shownfor five consecutive cycles (e.g., periods) P1 P2 . . . P5. During thefirst cycle P1, switches S1 and S2 are toggled as explained with respectto phases 100C through 100F of FIGS. 1C through 1F, and the switches S3and S4 are set at position A, to allow capacitors C3 and C4 be connectedin series with the capacitors C1 and C2, thereby providing the highamplitude triangular waveform, as shown by waveform 222. The amplitudeof the triangular waveform may be reduced by removing the capacitors C3and C4 from the circuit 200A, thereby providing smaller voltage to drivethe inductor current through the inductor L. This is done at cycle P2,where the switches S3 and S4 are both set to position B and switches S1and S2 go through the phases to generate a triangular waveform asexplained above. The ratio of amplitudes of the waveforms 222 and 224depend on the capacitance values of the capacitors C1, C2, C3, and C4.For example, if the capacitance values of the capacitors C1, C2, C3, andC4 are the same, the amplitude of the waveform 224 would be half of theamplitude of the waveform 222. Other amplitude ratios can be achieved bysuitably selecting the capacitance values of the capacitors C1, C2, C3,and C4.

During the third cycle P3, switches S1 and S2 are open and switches S3and S4 are set at position B, and the charged capacitors C1 have no pathfor driving current into the inductor L. Therefore, during cycle −P3,zero current passes through the inductor L. During this cycle, arecharge circuit (not shown for simplicity) can return the voltages ofcapacitors C1 and C2 to their desired level, correcting for resistivelosses, without generating a current in the inductor L and thereforewithout affecting the magnetic field. During the cycles P4 and P5, thesetting of switches S3 and S4 are the same as cycles P1 and P2, but thestatus of switches S1 and S2 in cycles P4 and P5 are reversed relativeto cycles P1 and P2, respectively. As a consequence, the direction ofcurrents in the inductor L are also reversed, resulting in waveforms 226and 228, which have the same amplitudes as their respective waveforms222 and 224, but with opposite polarities.

The waveforms 222, 224, 226, and 228 can be used to represent, forexample, binary symbols 11, 10, 01, and 00 by a magnetic communicationstransmitter using the circuit 200A as the magnetic field generator. Thecycle P3, which has no signal, can be used as the OFF symbol to allowfor calibration, synchronization, and background cancellation in thereceiver side.

FIGS. 3A-3B are diagrams illustrating examples of an H-bridge magneticwaveform generator circuit 300A and an H-bridge magnetic waveformgenerator circuit 300B with amplitude modulation capability, accordingto certain embodiments. The bridge magnetic waveform generator circuit300A (hereinafter “circuit 300A”) is similar to circuit 100A of FIG. 1A,except for the additional switches S3 and S2 and diodes D2 and D3 andthe fact that node 308 of the inductor L is not connected to the groundpotential. The switch S3 is coupled between nodes 304 and 308, andswitch S2 is coupled between nodes 308 and 306. Diodes D2 and D3 arecoupled in parallel with switches S3 and S2, respectively. Thecapacitors C1 and C2 join at node 310 that is coupled to groundpotential. In the circuit 300A, the drive circuitry, protectioncircuitry, power supplies, and internal resistors (e.g., for theinductor L) are not shown for simplicity. Switches S2 and S3 and diodesD2 and D3 can be implemented in the same semiconductor chip usingtransistor switches and semiconductor (e.g., silicon) diodes.

The configuration of FIG. 300A has the advantageous feature that allowsusing lower supply voltage values. For example, the capacitors C1 and C2can each be precharged to 50V (instead of 100V for circuit 100A) and thecircuit 300A still provides the same amplitude triangular waveform forthe current in the inductor L. The operation of the circuit 300Aincludes four phases, during which status of switches S1, S2, S3, and S4are controlled to be different to allow suitable paths for flow ofcurrent from or to the capacitors C1 and C2 through the inductor L.

During a first phase, switches S1 and S2 are closed and switches S3 andS4 are open, and diodes D1 and D2 are reverse biased. During the firstphase, the capacitors C1 and C2 discharge to drive a positive increasing(up-ramping) current through the switches S1 and S2 and the inductor L.This current provides the first quarter-cycle of a triangular currentwaveform (e.g., 120 of FIG. 1B). During a second phase, switches S1, S2,S3, and S4 are open, and diodes D1 and D2 are forward biased and conductcurrent. During this phase, the capacitors C1 and C2 recharge, whichcauses driving a positive decreasing (down-ramping) current through thediodes D1 and D2 into the inductor L. This current provides the secondquarter-cycle of the triangular current waveform.

During a third phase, switches S3 and S4 are closed and switches S1 andS2 are open, and diodes D1 and D2 are reverse biased. During this phase,the capacitors C1 and C2 discharge to drive a negative (e.g., withrevered direction) increasing amplitude current through the switches S3and S4 and the inductor L. This current provides the third quarter-cycleof the triangular current waveform. During a fourth phase, switches S1,S2, S3, and S4 are open, and diodes D3 and D4 are forward biased andconduct current. During this phase, the capacitors C1 and C2 rechargeand cause driving a negative decreasing current into the inductor Lthrough diodes D3 and D4. This current provides the fourth quarter-cycleof the triangular current waveform. The circuit 300A can be modified toprovide amplitude modulation as discussed herein.

The H-bridge magnetic waveform generator circuit 300B (hereinafter“circuit 300B”) shown in FIG. 3B has amplitude modulation capability.The circuit 300B has a portion 350 that is similar to the circuit 300Aand an additional portion 352 including an inductor L2, diodes D5 andD6, and switches S5 and S6. Here, the inductor L2 does not create anexternal magnetic field at long distances as, for example, a toroidalinductor. Whereas the inductor L1 creates an external magnetic waveformas, for example, a magnetic coil. The operation of portion 350 is alsosimilar to the operation of circuit 300A, as discussed above. Theportion 350 is used to generate a high (e.g., maximum)—amplitudetriangular current waveform (e.g., 222 of FIG. 2B), during the fourphased as discussed above with respect to FIG. 3A. During these phasesswitches S5 and S6 are open. When generating a low-amplitude triangularcurrent waveform (e.g., 224 of FIG. 2B), the portion 352 comes into theplay and switches S5 and S6 are suitably opened or closed (while S1 andS4 are kept open) to allow driving currents in two different directions,as explained above, into series connected inductors L1 and L2. Theseries connection of inductors L1 and L2 increases the impedance in thepath of the current and thereby decrease the amplitude of the currentpassing through the inductors L1 and L2. The ratio of amplitudes of thelow-amplitude and high-amplitude waveforms depend on the inductancevalues of the inductors L1 and L2. For example, if the inductance valuesof the inductors L1 and L2 are the same, the amplitude of thelow-amplitude waveform would be half of the amplitude of thehigh-amplitude waveform. Other amplitude ratios can be achieved bysuitably selecting the inductance values of the inductors L1 and L2.

FIG. 4 is a diagram illustrating an example of a method 400 forproviding a magnetic waveform generator circuit, according to certainembodiments. According to the method 400, a first switch (e.g., S1 ofFIG. 1A) is coupled, at a first node (e.g., 102 of FIG. 1A), to a firstrectifier element (e.g., D1 of FIG. 1A) (410). A first capacitor (e.g.,C1 of FIG. 1A) is coupled, at a second node (e.g., 104 of FIG. 1A) tothe first switch, and to a fourth node (e.g., 108 of FIG. 1A) (420). Asecond capacitor may be coupled, at a third node (e.g., 106 of FIG. 1A)to the first rectifier element, and to the forth node (430). An inductor(e.g., L of FIG. 1A) may be coupled between the first and the fourthnodes (440). The first switch is operable to be in an ON state during afirst time period (e.g., T1 of FIG. 1B) and in an off state during asecond time period (e.g., T2 of FIG. 1B). The first switch and the firstrectifier element are configured to enable the inductor to generate,during the first and the second time periods, a magnetic field having awaveform resembling a positive half-cycle of a triangular waveform(e.g., 120 of FIG. 1B).

Although the invention has been described with reference to thedisclosed embodiments, one having ordinary skill in the art will readilyappreciate that these embodiments are only illustrative of theinvention. It should be understood that various modifications can bemade without departing from the spirit of the invention. The particularembodiments disclosed above are illustrative only, as the presentinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Furthermore, no limitations are intended to thedetails of construction or design herein shown, other than as describedin the claims below. It is therefore evident that the particularillustrative embodiments disclosed above may be altered, combined, ormodified and all such variations are considered within the scope andspirit of the present invention. While compositions and methods aredescribed in terms of “comprising,” “containing,” or “including” variouscomponents or steps, the compositions and methods can also “consistessentially of” or “consist of” the various components and operations.All numbers and ranges disclosed above can vary by some amount. Whenevera numerical range with a lower limit and an upper limit is disclosed,any number and any subrange falling within the broader range isspecifically disclosed. Also, the terms in the claims have their plain,ordinary meaning unless otherwise explicitly and clearly defined by thepatentee. If there is any conflict in the usages of a word or term inthis specification and one or more patent or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

What is claimed is the following:
 1. A magnetic waveform generatorcircuit, the circuit comprising: a first switch coupled to a firstrectifier element at a first node; a first dipole switch coupled to thefirst switch at a second node; a first capacitor and a third capacitorcoupled to the first dipole switch and to a fourth node, the firstdipole switch coupled to the first capacitor in a first state and to thefirst capacitor and the third capacitor in series in a second state; asecond switch coupled to a second rectifier element at the first node; asecond dipole switch coupled to the second switch at a third node; asecond capacitor and a fourth capacitor coupled to the second dipoleswitch and to the first capacitor at the fourth node, the second dipoleswitch coupled to the second capacitor in a first state and to thesecond capacitor and the fourth capacitor in series in a second state;an inductor coupled between the first and the fourth nodes; wherein: thefirst switch and the first rectifier element are configured to enablethe inductor to generate, during a first time period and a second timeperiod, a magnetic field having a waveform resembling a positivehalf-cycle of a triangular waveform, the second switch and the secondrectifier element are configured to enable the inductor to generate,during a third time period and a fourth time period, a magnetic fieldhaving a waveform resembling a negative half-cycle of the triangularwaveform, the first dipole switch is operable, in the second state, tocouple the second node through the third capacitor to the firstcapacitor, and the second dipole switch is operable, in the secondstate, to couple the third node through the fourth capacitor to thesecond capacitor to generate a high amplitude triangular magnetic fieldwaveform.
 2. The circuit of claim 1, wherein the first switch or thesecond switch is a transistor.
 3. The circuit of claim 1, wherein thefirst rectifier element or the second rectifier element is a diode. 4.The circuit of claim 1, wherein during the first time period the firstswitch is open and the second switch is closed.
 5. The circuit of claim1, wherein during the second time period the first switch and the secondswitch are open.
 6. The circuit of claim 1, wherein during the thirdtime period the first switch is open and the second switch is closed. 7.The circuit of claim 1, wherein during the fourth time period the firstswitch and the second switch are open.
 8. The circuit of claim 1 whereinthe first dipole switch, second dipole switch, third capacitor, andfourth capacitor generate a current in the inductor with an amplitudemodulated triangular waveform.
 9. A method for providing a magneticwaveform generator, the method comprising: coupling, at a first node, afirst switch to a first rectifier element; coupling a first dipoleswitch to the first switch at a second node; coupling a first capacitorand a third capacitor to the first dipole switch and to a fourth node,the first dipole switch coupled to the first capacitor in a first stateand to the first capacitor and the third capacitor in series in a secondstate; coupling second switch to a second rectifier element at the firstnode; coupling second dipole switch to the second switch at a thirdnode; coupling a second capacitor and a fourth capacitor to the seconddipole switch and to the first capacitor at the fourth node, the seconddipole switch coupled to the second capacitor in a first state and tothe second capacitor and the fourth capacitor in series in a secondstate; coupling an inductor between the first and the fourth nodes,wherein: the first switch and the first rectifier element are configuredto enable the inductor to generate, during a first time period and asecond time period, a magnetic field having a waveform resembling apositive half-cycle of a triangular waveform, the second switch and thesecond rectifier element configured to enable the inductor to generate,during a third time period and a fourth time period, a magnetic fieldhaving a waveform resembling a negative half-cycle of the triangularwaveform, the first dipole switch configured to be operable, in thesecond state, to couple the second node through the third capacitor tothe first capacitor, and the second dipole switch configured to beoperable, in the second state, to couple the third node through thefourth capacitor to the second capacitor to allow generation of a highamplitude triangular magnetic field waveform.
 10. The method of claim 9,wherein the first switch or the second switch is a transistor.
 11. Themethod of claim 9, wherein the first rectifier element or the secondrectifier element is a diode.
 12. The method of claim 9, wherein duringthe first time period the first switch is open and the second switch isclosed.
 13. The method of claim 9, wherein during the second time periodthe first switch and the second switch are open.
 14. The method of claim9, wherein during the third time period the first switch is open and thesecond switch is closed.
 15. The method of claim 9, wherein during thefourth time period the first switch and the second switch are open.